15.3.38 Modifying DO Variable

g77 should warn about modifying DO variables via EQUIVALENCE. (The internal information gathered to produce this warning might also be useful in setting the internal “doiter” flag for a variable or even array reference within a loop, since that might produce faster code someday.)

For example, this code is invalid, so g77 should warn about the invalid assignment to NOTHER:

     EQUIVALENCE (I, NOTHER)
     DO I = 1, 100
        IF (I.EQ. 10) NOTHER = 20
     END DO